<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
  <style>
    html{
      height: 100%;
    }
    body{
      height: 100%;
    }
    /* %是相对于父级的百分比 */
    .box{
      width: 50%;
      height: 50%;
      background-color: pink;
    }
  </style>
</head>
<body>
  <div class="box">布局</div>
</body>
</html>